Earphones typically available for use with portable (e.g., wearable) voice communication equipment are ill fitting, are not designed to couple tightly to the ear opening, and hence provide poor isolation from external audible noise. Headphones are available that cover the outer ear and provide better acoustic isolation, but they are generally bulky and unattractive, and poorly suited for use in many situations where portable voice communications devices are used. In addition, the failure of most earphones to provide sufficient acoustic isolation frequently results in the user compensating by raising the level of the sound, causing ear-overload distortion. The level of the sound relative to the external noise improves, but the quality of the sound is degraded.
Many earphones for use with voice communication equipment attach to the ear with a loop that fits over the top and around the rear of the outer ear, while others use a headband that fits over the top of or behind the head. A representative example of the loop approach is seen in the “EarWrap” by Jabra Corporation, while the model TL-DR140 “wisp.ear” by Sony Electronics is one example of an earphone using a headband. The loop and headband are designed to fit a wide variety of ear and head shapes and sizes, resulting in a poor fit for many users. The earphone with loop easily falls off of the ear, and prolonged use may cause physical irritation. The headband is not well suited for use with headwear and crushes the hair. Still other earphones are held in place using an earmold that fits within the concha, or an “earbud” which is wedged into the opening of the ear canal. Examples of earphones using an earmold method of attachment can be seen in the “2WayBud” and “2WayBoom” earphones manufactured by Jabra Corporation, while the model DR-EX150UP by Sony Electronics employs an earbud. These earphones are typically smaller than those held in place by a loop or headband, are generally less physically secure and are easily pulled from the ear by the attached cable, and afford the user no appreciable exclusion of external acoustic noise. The presence of the boom frequently used to position a microphone near the mouth of the user exacerbates the problem of poor fit and attachment to the ear, frequently causing the earphone to loosen and fall from the ear.
To eliminate problems caused by a microphone boom, many earphones for use with cellular telephones use a microphone positioned along the earphone cable near the mouth of the user. This arrangement provides some improvement over the typical earphone with microphone boom, but suffers from a lack of accuracy in microphone position, resulting in wide variations in the level of the user's voice. Users of such devices are frequently seen manipulating the earphone cable in order to position the microphone more accurately.
The cable that typically runs from the earphone to the associated electrical device may be a significant source of the noise plaguing a user. Longitudinal forces created when the earphone cable comes in contact with surrounding objects or with the clothing of the user are normally conducted along the cable to the earphone housing, where they are audible to the user. This can be an annoying source of noise.
An additional area for improvement relates to the receiver used within the earphone. Earphone receivers are typically designed to be driven from either a voltage source or a current source. In designing a voltage-driven receiver, many manufacturers select for the receiver electromagnet the largest diameter coil wire that will produce the required sound level within the available space. The use of the largest wire reduces the chance of wire breakage during manufacture, maximizing yield. This also results in a receiver with the lowest possible D.C. resistance. The receiver impedance varies over the range of operating frequencies, with the lowest impedance occurring at the lowest frequency. In a voltage-driven design, the largest coil current will occur at the lowest frequency, resulting in an earphone having an undesirable low-frequency boost. To reduce this effect, many manufacturers place a resistor in series with the receiver coil. This has several disadvantages including the cost of the resistor, the space required for the resistor, and possible failure of the resistor and its connections. It would be advantageous to find a way to eliminate the need for this resistor.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.